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S. Rosier-Lees

Publications and source records attributed to S. Rosier-Lees.

13 recordsLinked to original sources
arXiv2015

NectarCAM : a camera for the medium size telescopes of the Cherenkov Telescope Array

NectarCAM is a camera proposed for the medium-sized telescopes of the Cherenkov Telescope Array (CTA) covering the central energy range of ~100 GeV to ~30 TeV. It has a modular design and is based on the NECTAr chip, at the heart of which is a GHz sampling Switched Capacitor Array and a 12-bit Analog to Digital converter. The camera will be equipped with 265 7-photomultiplier modules, covering a field of view of 8 degrees. Each module includes the photomultiplier bases, high voltage supply, pre-amplifier, trigger, readout and Ethernet transceiver. The recorded events last between a few nanoseconds and tens of nanoseconds. The camera trigger will be flexible so as to minimize the read-out dead-time of the NECTAr chips. NectarCAM is designed to sustain a data rate of more than 4 kHz with less than 5\% dead time. The camera concept, the design and tests of the various subcomponents and results of thermal and electrical prototypes are presented. The design includes the mechanical structure, cooling of the electronics, read-out, clock distribution, slow control, data-acquisition, triggering, monitoring and services.

astro-ph.IM↗
arXiv2013

Improved sensitivity of H.E.S.S.-II through the fifth telescope focus system

The Imaging Atmospheric Cherenkov Telescope (IACT) works by imaging the very short flash of Cherenkov radiation generated by the cascade of relativistic charged particles produced when a TeV gamma ray strikes the atmosphere. This energetic air shower is initiated at an altitude of 10-30 km depending on the energy and the arrival direction of the primary gamma ray. Whether the best image of the shower is obtained by focusing the telescope at infinity and measuring the Cherenkov photon angles or focusing on the central region of the shower is a not obvious question. This is particularly true for large size IACT for which the depth of the field is much smaller. We address this issue in particular with the fifth telescope (CT5) of the High Energy Stereoscopic System (H.E.S.S.); a 28 m dish large size telescope recently entered in operation and sensitive to an energy threshold of tens of GeVs. CT5 is equipped with a focus system, its working principle and the expected effect of focusing depth on the telescope sensitivity at low energies (50-200 GeV) is discussed.

astro-ph.IM↗
arXiv2013

The NectarCAM camera project

In the framework of the next generation of Cherenkov telescopes, the Cherenkov Telescope Array (CTA), NectarCAM is a camera designed for the medium size telescopes covering the central energy range of 100 GeV to 30 TeV. NectarCAM will be finely pixelated (~ 1800 pixels for a 8 degree field of view, FoV) in order to image atmospheric Cherenkov showers by measuring the charge deposited within a few nanoseconds time-window. It will have additional features like the capacity to record the full waveform with GHz sampling for every pixel and to measure event times with nanosecond accuracy. An array of a few tens of medium size telescopes, equipped with NectarCAMs, will achieve up to a factor of ten improvement in sensitivity over existing instruments in the energy range of 100 GeV to 10 TeV. The camera is made of roughly 250 independent read-out modules, each composed of seven photo-multipliers, with their associated high voltage base and control, a read-out board and a multi-service backplane board. The read-out boards use NECTAr (New Electronics for the Cherenkov Telescope Array) ASICs which have the dual functionality of analogue memories and Analogue to Digital Converter (ADC). The camera trigger to be used will be flexible so as to minimize the read-out dead-time of the NECTAr chips. We present the camera concept and the design and tests of the various subcomponents. The design includes the mechanical parts, the cooling of the electronics, the readout, the data acquisition, the trigger, the monitoring and services.

astro-ph.IM↗
arXiv2013

The Cherenkov Telescope Array Large Size Telescope

The two arrays of the Very High Energy gamma-ray observatory Cherenkov Telescope Array (CTA) will include four Large Size Telescopes (LSTs) each with a 23 m diameter dish and 28 m focal distance. These telescopes will enable CTA to achieve a low-energy threshold of 20 GeV, which is critical for important studies in astrophysics, astroparticle physics and cosmology. This work presents the key specifications and performance of the current LST design in the light of the CTA scientific objectives.

astro-ph.IM↗
arXiv2012

The electromagnetic calorimeter of the AMS-02 experiment

The electromagnetic calorimeter (ECAL) of the AMS-02 experiment is a 3-dimensional sampling calorimeter, made of lead and scintillating fibers. The detector allows for a high granularity, with 18 samplings in the longitudinal direction, and 72 sampling in the lateral direction. The ECAL primary goal is to measure the energy of cosmic rays up to few TeV, however, thanks to the fine grained structure, it can also provide the separation of positrons from protons, in the GeV to TeV region. A direct measurement of high energy photons with accurate energy and direction determination can also be provided.

physics.ins-det↗
arXiv2010

Indirect search for dark matter with micrOMEGAs2.4

We present a new module of micrOMEGAs devoted to the computation of indirect signals from dark matter annihilation in any new model with a stable weakly interacting particle. The code provides the mass spectrum, cross-sections, relic density and exotic fluxes of gamma rays, positrons and antiprotons. The propagation of charged particles in the Galactic halo is handled with a new module that allows to easily modify the propagation parameters.

hep-ph↗
arXiv2010

Optimization of multivariate analysis for IACT stereoscopic systems

Multivariate methods have been recently introduced and successfully applied for the discrimination of signal from background in the selection of genuine very-high energy gamma-ray events with the H.E.S.S. Imaging Atmospheric Cerenkov Telescope. The complementary performance of three independent reconstruction methods developed for the H.E.S.S. data analysis, namely Hillas, model and 3D-model suggests the optimization of their combination through the application of a resulting efficient multivariate estimator. In this work the boosted decision tree method is proposed leading to a significant increase in the signal over background ratio compared to the standard approaches. The improved sensitivity is also demonstrated through a comparative analysis of a set of benchmark astrophysical sources.

astro-ph.IM↗
arXiv2006

An indirect dark matter search with diffuse gamma rays from the Galactic Centre with the Alpha Magnetic Spectrometer

The detection of non-baryonic dark matter through its gamma-ray annihilation in the centre of our galaxy has been studied. The gamma fluxes according to different models have been simulated and compared to those expected to be observed with the Alpha Magnetic Spectrometer (AMS), during a long-term mission on board of the International Space Station. Under the assumption that the dark matter halo is composed of the lightest, stable supersymmetric particle, the neutralino, the results of the simulations in the framework of mSUGRA models, show that with a cuspy dark matter halo or a clumpy halo, the annihilation gamma-ray signal would be detected by AMS. More optimistic perspectives are obtained with the Anomaly Mediated Supersymmetry Breaking (AMSB) model. The latter leads also to a cosmologically important 6Li abundance. Finally, the discovery potential for the massive Kaluza-Klein dark matter candidates has been evaluated and their detection looks feasible.

astro-ph↗
arXiv2006

AMS02 Ecal gamma trigger performance measured at the October 2004 CERN test beam

Test beam data collected in October 2004 at CERN PS to validate the AMS02 Ecal Intermediate Board (EIB) are analyzed. After describing the experimental setup and the event samples, results concerning noise measurement, trigger efficiency and threshold accuracy are presented. They demonstrate that the EIB fulfils the physics requirements. Therefore the analog part of the trigger is validated, and hardware choices are also made towards the final device.

astro-ph↗
arXiv2003

Lower limit on the neutralino mass in the general MSSM

We discuss constraints on SUSY models with non-unified gaugino masses and R_P conservation. We derive a lower bound on the neutralino mass combining the direct limits from LEP, the indirect limits from gmuon, bsgamma, Bsmumu and the relic density constraint from WMAP. The lightest neutralino (mneutralino=6GeV) is found in models with a light pseudoscalar with MA<200GeV and a large value for $tanβ$. Models with heavy pseudoscalars lead to mneutralino>18(29)GeV for $\tanβ=50(10)$. We show that even a very conservative bound from the muon anomalous magnetic moment can increase the lower bound on the neutralino mass in models with mu<0 and/or large values of $\tanβ$. We then examine the potential of the Tevatron and the direct detection experiments to probe the SUSY models with the lightest neutralinos allowed in the context of light pseudoscalars with high $\tanβ$. We also examine the potential of an e+e- collider of 500GeV to produce SUSY particles in all models with neutralinos lighter than the W. In contrast to the mSUGRA models, observation of at least one sparticle is not always guaranteed.

hep-ph↗
arXiv2000

SUSY Higgs at the LHC: Effects of light charginos and neutralinos

In view of the latest LEP data we consider the effects of charginos and neutralinos on the two-photon and bbbar signatures of the Higgs at the LHC. Assuming the usual GUT inspired relation between M_1 and M_2 we show that there are only small regions with moderate tanbeta and large stop mixings that may be dangerous. Pathological models not excluded by LEP which have degeneracy between the sneutrino and the chargino are however a real danger because of large branching fraction of the Higgs into invisibles. We have also studied models where the gaugino masses are not unified at the GUT scale. We take M_1=M_2/10 as an example where large reductions in the signal at the LHC can occur. However we argue that such models with a very light neutralino LSP may give a too large relic density unless the sleptons are light. We then combine this cosmological constraint with neutralino production with light sfermions to further reduce the parameter space that precludes observability of the Higgs at the LHC. We still find regions of parameter space where the drops in the usual Higgs signals at the LHC can be drastic. Nonetheless, in such scenarios where Higgs may escape detection we show that one should be able to produce all charginos and neutralinos. Although the heavier of these could cascade into the Higgs, the rates are not too high and the Higgs may not always be recovered this way.

hep-ph↗